The present invention relates to sewing machines in general, and more particularly to improvements in presser feet for use in sewing machines. Still more particularly, the invention relates to improvements in self-adjusting presser feet, namely to presser feet wherein the sole plate is movable with reference to the shank.
The purpose of the presser foot is to urge the material being sewn toward the feed dog. The shank of the presser foot is secured to the presser bar of the sewing machine and its lower end portion carries the sole plate. As a rule, the sole plate is pivotable with reference to the shank about an axis which extends at right angles to the direction of advancement of the work when the sewing machine is in use. It is also known to provide the presser foot with a readily detachable sole plate so that the latter can be replaced with a differently configurated sole plate, e.g., for the sewing of zippers, buttons, buttonholes and others. The purpose of a movably mounted sole plate is to enable it to ride over transverse stitches and/or to permit workpiece portions of different thicknesses to advance toward, above and beyond the feed dog. If the sole plate is mounted for pivotal movement about a single axis, such axis is preferably horizontal and extends at right angles to the direction of advancement of the work.
Swiss Pat. No. 369,009 discloses a presser foot wherein the sole plate is free to perform limited movements with reference to the shank. The means for limiting such movements about a transversely extending axis includes a stud which is provided on the sole plate and extends with play into a bore of the shank. The just described presser foot is quite satisfactory when it suffices to mount the sole plate with freedom of movement about a single axis. However, it is often desirable and advantageous to enable the sole plate to perform more complex movements relative to the shank. Such movements can be performed if the sole plate is mounted in a manner as disclosed in U.S. Pat. No. 3,304,896 to Laidig. This patent teaches to mount the sole plate for pivotal movement relative to a U-shaped yoke and to mount the yoke for pivotal movement relative to the shank. The pivot axis of the sole plate extends at right angles to the direction of movement of the work and at right angles to the pivot axis of the yoke. Both pivot axes are horizontal and they do not intersect each other. A drawback of the proposal of Laidig is that the patented presser foot comprises a large number of rather complex parts which contributes to the initial cost as well as to the cost of assembling the parts of the presser foot and of mounting the assembled parts on the presser bar. Furthermore, the yoke is likely to jam in response to transfer of forces from the shank to the sole plate so that it cannot turn relative to the shank. Moreover, the pivot axis of the yoke is located at a level well above the pivot axis of the sole plate so that the sole plate is free to perform pronounced lateral movements in response to pivoting of the yoke with reference to the shank. Still further, the means for limiting the extent of pivotal movement of the yoke relative to the shank and the means for limiting the extent of pivotal movement of the sole plate relative to the yoke each comprise a substantial number of parts which must be machined with a high degree of precision and are likely to fail in response to contamination when the sewing machine is in use. This applies especially for the means which limits the extent of movability of the yoke relative to the shank and comprises a tilt stop rivet whose head is adjacent to the front side of the central panel of the yoke and whose shank extends with some play through a first hole in such central panel and without play into a second hole which is provided in the lower portion of the shank.